Runnable
ForkJoinWorkerThread
public class Thread extends Object implements Runnable
Thread
defines constructors and a Thread.Builder
to create threads. Starting a thread schedules it to execute its run
method. The newly started thread executes concurrently with the thread that caused it to start.
A thread terminates if either its run
method completes normally, or if its run
method completes abruptly and the appropriate uncaught exception handler completes normally or abruptly. With no code left to run, the thread has completed execution. The join
method can be used to wait for a thread to terminate.
Threads have a unique identifier and a name. The identifier is generated when a Thread
is created and cannot be changed. The thread name can be specified when creating a thread or can be changed at a later time.
Threads support ThreadLocal
variables. These are variables that are local to a thread, meaning a thread can have a copy of a variable that is set to a value that is independent of the value set by other threads. Thread
also supports InheritableThreadLocal
variables that are thread local variables that are inherited at thread creation time from the parent Thread
. Thread
supports a special inheritable thread local for the thread context-class-loader.
Thread
supports the creation of platform threads that are typically mapped 1:1 to kernel threads scheduled by the operating system. Platform threads will usually have a large stack and other resources that are maintained by the operating system. Platforms threads are suitable for executing all types of tasks but may be a limited resource.
Platform threads get an automatically generated thread name by default.
Platform threads are designated daemon or non-daemon threads. When the Java virtual machine starts up, there is usually one non-daemon thread (the thread that typically calls the application's main
method). The shutdown sequence begins when all started non-daemon threads have terminated. Unstarted non-daemon threads do not prevent the shutdown sequence from beginning.
In addition to the daemon status, platform threads have a thread priority and are members of a thread group.
Thread
also supports the creation of virtual threads. Virtual threads are typically user-mode threads scheduled by the Java runtime rather than the operating system. Virtual threads will typically require few resources and a single Java virtual machine may support millions of virtual threads. Virtual threads are suitable for executing tasks that spend most of the time blocked, often waiting for I/O operations to complete. Virtual threads are not intended for long running CPU intensive operations.
Virtual threads typically employ a small set of platform threads used as carrier threads. Locking and I/O operations are examples of operations where a carrier thread may be re-scheduled from one virtual thread to another. Code executing in a virtual thread is not aware of the underlying carrier thread. The currentThread() method, used to obtain a reference to the current thread, will always return the Thread
object for the virtual thread.
Virtual threads do not have a thread name by default. The getName
method returns the empty string if a thread name is not set.
Virtual threads are daemon threads and so do not prevent the shutdown sequence from beginning. Virtual threads have a fixed thread priority that cannot be changed.
Thread
defines public constructors for creating platform threads and the start
method to schedule threads to execute. Thread
may be extended for customization and other advanced reasons although most applications should have little need to do this.
Thread
defines a Thread.Builder
API for creating and starting both platform and virtual threads. The following are examples that use the builder:
Runnable runnable = ...
// Start a daemon thread to run a task
Thread thread = Thread.ofPlatform().daemon().start(runnable);
// Create an unstarted thread with name "duke", its start() method
// must be invoked to schedule it to execute.
Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);
// A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
// Start a virtual thread to run a task
Thread thread = Thread.ofVirtual().start(runnable);
// A ThreadFactory that creates virtual threads
ThreadFactory factory = Thread.ofVirtual().factory();
Thread
inherits its initial values of inheritable-thread-local variables (including the context class loader) from the parent thread values at the time that the child Thread
is created. The 5-param constructor can be used to create a thread that does not inherit its initial values from the constructing thread. When using a Thread.Builder
, the inheritInheritableThreadLocals
method can be used to select if the initial values are inherited. Platform threads inherit the daemon status, thread priority, and when not provided (or not selected by a security manager), the thread group.
Creating a platform thread captures the caller context to limit the permissions of the new thread when it executes code that performs a privileged action. The captured caller context is the new thread's "Inherited AccessControlContext
". Creating a virtual thread does not capture the caller context; virtual threads have no permissions when executing code that performs a privileged action.
Unless otherwise specified, passing a null
argument to a constructor or method in this class will cause a NullPointerException
to be thrown.
System property | Description |
---|---|
jdk.virtualThreadScheduler.parallelism | The number of platform threads available for scheduling virtual threads. It defaults to the number of available processors. |
jdk.virtualThreadScheduler.maxPoolSize | The maximum number of platform threads available to the scheduler. It defaults to 256. |
Modifier and Type | Class | Description |
---|---|---|
static interface |
Thread.Builder |
A builder for Thread and ThreadFactory objects. |
static enum |
Thread.State |
A thread state. |
static interface |
Thread.UncaughtExceptionHandler |
Interface for handlers invoked when a Thread abruptly terminates due to an uncaught exception. |
Modifier and Type | Field | Description |
---|---|---|
static final int |
MAX_PRIORITY |
The maximum priority that a thread can have. |
static final int |
MIN_PRIORITY |
The minimum priority that a thread can have. |
static final int |
NORM_PRIORITY |
The default priority that is assigned to a thread. |
Constructor | Description |
---|---|
Thread() |
Initializes a new platform Thread . |
Thread |
Initializes a new platform Thread . |
Thread |
Initializes a new platform Thread . |
Thread |
Initializes a new platform Thread . |
Thread |
Initializes a new platform Thread . |
Thread |
Initializes a new platform Thread so that it has task as its run object, has the specified name as its name, and belongs to the thread group referred to by group . |
Thread |
Initializes a new platform Thread so that it has task as its run object, has the specified name as its name, and belongs to the thread group referred to by group , and has the specified stack size. |
Thread |
Initializes a new platform Thread so that it has task as its run object, has the specified name as its name, belongs to the thread group referred to by group , has the specified stackSize , and inherits initial values for inheritable thread-local variables if inheritThreadLocals is true . |
Thread |
Initializes a new platform Thread . |
Modifier and Type | Method | Description |
---|---|---|
static int |
activeCount() |
Returns an estimate of the number of live platform threads in the current thread's thread group and its subgroups. |
final void |
checkAccess() |
Deprecated, for removal: This API element is subject to removal in a future version. This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. |
protected Object |
clone() |
Throws CloneNotSupportedException as a Thread can not be meaningfully cloned. |
int |
countStackFrames() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally designed to count the number of stack frames but the results were never well-defined and it depended on thread-suspension. |
static Thread |
currentThread() |
Returns the Thread object for the current thread. |
static void |
dumpStack() |
Prints a stack trace of the current thread to the standard error stream. |
static int |
enumerate |
Copies into the specified array every live platform thread in the current thread's thread group and its subgroups. |
static Map |
getAllStackTraces() |
Returns a map of stack traces for all live platform threads. |
ClassLoader |
getContextClassLoader() |
Returns the context ClassLoader for this thread. |
static Thread.UncaughtExceptionHandler |
getDefaultUncaughtExceptionHandler() |
Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception. |
long |
getId() |
Deprecated. This method is not final and may be overridden to return a value that is not the thread ID. |
final String |
getName() |
Returns this thread's name. |
final int |
getPriority() |
Returns this thread's priority. |
StackTraceElement[] |
getStackTrace() |
Returns an array of stack trace elements representing the stack dump of this thread. |
Thread.State |
getState() |
Returns the state of this thread. |
final ThreadGroup |
getThreadGroup() |
Returns the thread's thread group or null if the thread has terminated. |
Thread.UncaughtExceptionHandler |
getUncaughtExceptionHandler() |
Returns the handler invoked when this thread abruptly terminates due to an uncaught exception. |
static boolean |
holdsLock |
Returns true if and only if the current thread holds the monitor lock on the specified object. |
void |
interrupt() |
Interrupts this thread. |
static boolean |
interrupted() |
Tests whether the current thread has been interrupted. |
final boolean |
isAlive() |
Tests if this thread is alive. |
final boolean |
isDaemon() |
Tests if this thread is a daemon thread. |
boolean |
isInterrupted() |
Tests whether this thread has been interrupted. |
final boolean |
isVirtual() |
Returns true if this thread is a virtual thread. |
final void |
join() |
Waits for this thread to terminate. |
final void |
join |
Waits at most millis milliseconds for this thread to terminate. |
final void |
join |
Waits at most millis milliseconds plus nanos nanoseconds for this thread to terminate. |
final boolean |
join |
Waits for this thread to terminate for up to the given waiting duration. |
static Thread.Builder.OfPlatform |
ofPlatform() |
Returns a builder for creating a platform Thread or ThreadFactory that creates platform threads. |
static Thread.Builder.OfVirtual |
ofVirtual() |
Returns a builder for creating a virtual Thread or ThreadFactory that creates virtual threads. |
static void |
onSpinWait() |
Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities. |
final void |
resume() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to resume a thread suspended with suspend() . |
void |
run() |
This method is run by the thread when it executes. |
void |
setContextClassLoader |
Sets the context ClassLoader for this thread. |
final void |
setDaemon |
Marks this thread as either a daemon or non-daemon thread. |
static void |
setDefaultUncaughtExceptionHandler |
Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread. |
final void |
setName |
Changes the name of this thread to be equal to the argument name . |
final void |
setPriority |
Changes the priority of this thread. |
void |
setUncaughtExceptionHandler |
Set the handler invoked when this thread abruptly terminates due to an uncaught exception. |
static void |
sleep |
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. |
static void |
sleep |
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers. |
static void |
sleep |
Causes the currently executing thread to sleep (temporarily cease execution) for the specified duration, subject to the precision and accuracy of system timers and schedulers. |
void |
start() |
Schedules this thread to begin execution. |
static Thread |
startVirtualThread |
Creates a virtual thread to execute a task and schedules it to execute. |
final void |
stop() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to "stop" a victim thread by causing the victim thread to throw a ThreadDeath . |
final void |
suspend() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to suspend a thread. |
final long |
threadId() |
Returns the identifier of this Thread. |
String |
toString() |
Returns a string representation of this thread. |
static void |
yield() |
A hint to the scheduler that the current thread is willing to yield its current use of a processor. |
public static final int MIN_PRIORITY
public static final int NORM_PRIORITY
public static final int MAX_PRIORITY
public Thread()
Thread
. This constructor has the same effect as Thread (null, null, gname)
, where gname
is a newly generated name. Automatically generated names are of the form "Thread-"+
n, where n is an integer. This constructor is only useful when extending Thread
to override the run()
method.
public Thread(Runnable task)
Thread
. This constructor has the same effect as Thread (null, task, gname)
, where gname
is a newly generated name. Automatically generated names are of the form "Thread-"+
n, where n is an integer. For a non-null task, invoking this constructor directly is equivalent to:
Thread.ofPlatform().unstarted(task);
task
- the object whose run
method is invoked when this thread is started. If null
, this classes run
method does nothing.public Thread(ThreadGroup group, Runnable task)
Thread
. This constructor has the same effect as Thread (group, task, gname)
, where gname
is a newly generated name. Automatically generated names are of the form "Thread-"+
n, where n is an integer. For a non-null group and task, invoking this constructor directly is equivalent to:
Thread.ofPlatform().group(group).unstarted(task);
group
- the thread group. If null
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or
SecurityManager.getThreadGroup()
returns null
, the group is set to the current thread's thread group.task
- the object whose run
method is invoked when this thread is started. If null
, this thread's run method is invoked.SecurityException
- if the current thread cannot create a thread in the specified thread grouppublic Thread(String name)
Thread
. This constructor has the same effect as Thread (null, null, name)
. This constructor is only useful when extending Thread
to override the run()
method.
name
- the name of the new threadpublic Thread(ThreadGroup group, String name)
Thread
. This constructor has the same effect as Thread (group, null, name)
. This constructor is only useful when extending Thread
to override the run()
method.
group
- the thread group. If null
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or
SecurityManager.getThreadGroup()
returns null
, the group is set to the current thread's thread group.name
- the name of the new threadSecurityException
- if the current thread cannot create a thread in the specified thread grouppublic Thread(Runnable task, String name)
Thread
. This constructor has the same effect as Thread (null, task, name)
. For a non-null task and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform().name(name).unstarted(task);
task
- the object whose run
method is invoked when this thread is started. If null
, this thread's run method is invoked.name
- the name of the new threadpublic Thread(ThreadGroup group, Runnable task, String name)
Thread
so that it has task
as its run object, has the specified name
as its name, and belongs to the thread group referred to by group
. If there is a security manager, its checkAccess
method is invoked with the ThreadGroup as its argument.
In addition, its checkPermission
method is invoked with the RuntimePermission("enableContextClassLoaderOverride")
permission when invoked directly or indirectly by the constructor of a subclass which overrides the getContextClassLoader
or setContextClassLoader
methods.
The priority of the newly created thread is the smaller of priority of the thread creating it and the maximum permitted priority of the thread group. The method setPriority may be used to change the priority to a new value.
The newly created thread is initially marked as being a daemon thread if and only if the thread creating it is currently marked as a daemon thread. The method setDaemon may be used to change whether or not a thread is a daemon.
For a non-null group, task, and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform().group(group).name(name).unstarted(task);
group
- the thread group. If null
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or
SecurityManager.getThreadGroup()
returns null
, the group is set to the current thread's thread group.task
- the object whose run
method is invoked when this thread is started. If null
, this thread's run method is invoked.name
- the name of the new threadSecurityException
- if the current thread cannot create a thread in the specified thread group or cannot override the context class loader methods.public Thread(ThreadGroup group, Runnable task, String name, long stackSize)
Thread
so that it has task
as its run object, has the specified name
as its name, and belongs to the thread group referred to by group
, and has the specified stack size. This constructor is identical to Thread(ThreadGroup,Runnable,String)
with the exception of the fact that it allows the thread stack size to be specified. The stack size is the approximate number of bytes of address space that the virtual machine is to allocate for this thread's stack. The effect of the stackSize
parameter, if any, is highly platform dependent.
On some platforms, specifying a higher value for the stackSize
parameter may allow a thread to achieve greater recursion depth before throwing a StackOverflowError
. Similarly, specifying a lower value may allow a greater number of threads to exist concurrently without throwing an OutOfMemoryError
(or other internal error). The details of the relationship between the value of the stackSize
parameter and the maximum recursion depth and concurrency level are platform-dependent. On some platforms, the value of the stackSize
parameter may have no effect whatsoever.
The virtual machine is free to treat the stackSize
parameter as a suggestion. If the specified value is unreasonably low for the platform, the virtual machine may instead use some platform-specific minimum value; if the specified value is unreasonably high, the virtual machine may instead use some platform-specific maximum. Likewise, the virtual machine is free to round the specified value up or down as it sees fit (or to ignore it completely).
Specifying a value of zero for the stackSize
parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String)
constructor.
Due to the platform-dependent nature of the behavior of this constructor, extreme care should be exercised in its use. The thread stack size necessary to perform a given computation will likely vary from one JRE implementation to another. In light of this variation, careful tuning of the stack size parameter may be required, and the tuning may need to be repeated for each JRE implementation on which an application is to run.
Implementation note: Java platform implementers are encouraged to document their implementation's behavior with respect to the stackSize
parameter.
For a non-null group, task, and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform().group(group).name(name).stackSize(stackSize).unstarted(task);
group
- the thread group. If null
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or
SecurityManager.getThreadGroup()
returns null
, the group is set to the current thread's thread group.task
- the object whose run
method is invoked when this thread is started. If null
, this thread's run method is invoked.name
- the name of the new threadstackSize
- the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.SecurityException
- if the current thread cannot create a thread in the specified thread grouppublic Thread(ThreadGroup group, Runnable task, String name, long stackSize, boolean inheritInheritableThreadLocals)
Thread
so that it has task
as its run object, has the specified name
as its name, belongs to the thread group referred to by group
, has the specified stackSize
, and inherits initial values for inheritable thread-local variables if inheritThreadLocals
is true
. This constructor is identical to Thread(ThreadGroup,Runnable,String,long)
with the added ability to suppress, or not, the inheriting of initial values for inheritable thread-local variables from the constructing thread. This allows for finer grain control over inheritable thread-locals. Care must be taken when passing a value of false
for inheritThreadLocals
, as it may lead to unexpected behavior if the new thread executes code that expects a specific thread-local value to be inherited.
Specifying a value of true
for the inheritThreadLocals
parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String, long)
constructor.
For a non-null group, task, and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform()
.group(group)
.name(name)
.stackSize(stackSize)
.inheritInheritableThreadLocals(inheritInheritableThreadLocals)
.unstarted(task);
group
- the thread group. If null
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or
SecurityManager.getThreadGroup()
returns null
, the group is set to the current thread's thread group.task
- the object whose run
method is invoked when this thread is started. If null
, this thread's run method is invoked.name
- the name of the new threadstackSize
- the desired stack size for the new thread, or zero to indicate that this parameter is to be ignoredinheritInheritableThreadLocals
- if true
, inherit initial values for inheritable thread-locals from the constructing thread, otherwise no initial values are inheritedSecurityException
- if the current thread cannot create a thread in the specified thread grouppublic static Thread currentThread()
public static void yield()
Yield is a heuristic attempt to improve relative progression between threads that would otherwise over-utilise a CPU. Its use should be combined with detailed profiling and benchmarking to ensure that it actually has the desired effect.
It is rarely appropriate to use this method. It may be useful for debugging or testing purposes, where it may help to reproduce bugs due to race conditions. It may also be useful when designing concurrency control constructs such as the ones in the java.util.concurrent.locks
package.
public static void sleep(long millis) throws InterruptedException
millis
- the length of time to sleep in millisecondsIllegalArgumentException
- if the value of millis
is negativeInterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public static void sleep(long millis, int nanos) throws InterruptedException
millis
- the length of time to sleep in millisecondsnanos
- 0-999999
additional nanoseconds to sleepIllegalArgumentException
- if the value of millis
is negative, or the value of nanos
is not in the range 0-999999
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public static void sleep(Duration duration) throws InterruptedException
duration
- the duration to sleepInterruptedException
- if the current thread is interrupted while sleeping. The interrupted status of the current thread is cleared when this exception is thrown.public static void onSpinWait()
onSpinWait
method should be placed inside the spin loop. class EventHandler {
volatile boolean eventNotificationNotReceived;
void waitForEventAndHandleIt() {
while ( eventNotificationNotReceived ) {
Thread.onSpinWait();
}
readAndProcessEvent();
}
void readAndProcessEvent() {
// Read event from some source and process it
. . .
}
}
The code above would remain correct even if the onSpinWait
method was not called at all. However on some architectures the Java Virtual Machine may issue the processor instructions to address such code patterns in a more beneficial way.
public static Thread.Builder.OfPlatform ofPlatform()
Thread
or ThreadFactory
that creates platform threads. Interaction with security manager when creating platform threads
Creating a platform thread when there is a security manager set will invoke the security manager's checkAccess(ThreadGroup)
method with the thread's thread group. If the thread group has not been set with the OfPlatform.group
method then the security manager's getThreadGroup
method will be invoked first to select the thread group. If the security manager getThreadGroup
method returns null
then the thread group of the constructing thread is used.
// Start a daemon thread to run a task
Thread thread = Thread.ofPlatform().daemon().start(runnable);
// Create an unstarted thread with name "duke", its start() method
// must be invoked to schedule it to execute.
Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);
// A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
Thread
or ThreadFactory
objects.public static Thread.Builder.OfVirtual ofVirtual()
Thread
or ThreadFactory
that creates virtual threads. // Start a virtual thread to run a task.
Thread thread = Thread.ofVirtual().start(runnable);
// A ThreadFactory that creates virtual threads
ThreadFactory factory = Thread.ofVirtual().factory();
Thread
or ThreadFactory
objects.protected Object clone() throws CloneNotSupportedException
clone
in class Object
CloneNotSupportedException
- alwayspublic static Thread startVirtualThread(Runnable task)
This method is equivalent to:
Thread.ofVirtual().start(task);
task
- the object to run when the thread executespublic final boolean isVirtual()
true
if this thread is a virtual thread. A virtual thread is scheduled by the Java virtual machine rather than the operating system.true
if this thread is a virtual threadpublic void start()
A thread can be started at most once. In particular, a thread can not be restarted after it has terminated.
IllegalThreadStateException
- if the thread was already startedpublic void run()
Thread
may override this method. This method is not intended to be invoked directly. If this thread is a platform thread created with a Runnable
task then invoking this method will invoke the task's run
method. If this thread is a virtual thread then invoking this method directly does nothing.
@Deprecated(since="1.2", forRemoval=true) public final void stop()
ThreadDeath
. It was inherently unsafe. Stopping a thread caused it to unlock all of the monitors that it had locked (as a natural consequence of the ThreadDeath
exception propagating up the stack). If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects became visible to other threads, potentially resulting in arbitrary behavior. Usages of stop
should be replaced by code that simply modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run method in an orderly fashion if the variable indicates that it is to stop running. If the target thread waits for long periods (on a condition variable, for example), the interrupt
method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.UnsupportedOperationException
.UnsupportedOperationException
- alwayspublic void interrupt()
Unless the current thread is interrupting itself, which is always permitted, the checkAccess
method of this thread is invoked, which may cause a SecurityException
to be thrown.
If this thread is blocked in an invocation of the wait()
, wait(long)
, or wait(long, int)
methods of the Object
class, or of the join()
, join(long)
, join(long, int)
, sleep(long)
, or sleep(long, int)
methods of this class, then its interrupt status will be cleared and it will receive an InterruptedException
.
If this thread is blocked in an I/O operation upon an InterruptibleChannel
then the channel will be closed, the thread's interrupt status will be set, and the thread will receive a ClosedByInterruptException
.
If this thread is blocked in a Selector
then the thread's interrupt status will be set and it will return immediately from the selection operation, possibly with a non-zero value, just as if the selector's wakeup
method were invoked.
If none of the previous conditions hold then this thread's interrupt status will be set.
Interrupting a thread that is not alive need not have any effect.
interrupted()
and isInterrupted()
.SecurityException
- if the current thread cannot modify this threadpublic static boolean interrupted()
true
if the current thread has been interrupted; false
otherwise.public boolean isInterrupted()
true
if this thread has been interrupted; false
otherwise.public final boolean isAlive()
true
if this thread is alive; false
otherwise.@Deprecated(since="1.2", forRemoval=true) public final void suspend()
resume
, deadlock would result. Such deadlocks typically manifested themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.UnsupportedOperationException
.UnsupportedOperationException
- always@Deprecated(since="1.2", forRemoval=true) public final void resume()
suspend()
. Suspending a thread was inherently deadlock-prone. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.UnsupportedOperationException
.UnsupportedOperationException
- alwayspublic final void setPriority(int newPriority)
newPriority
and the maximum permitted priority of the thread's thread group. The priority of a virtual thread is always NORM_PRIORITY
and newPriority
is ignored.newPriority
- the new thread priorityIllegalArgumentException
- if the priority is not in the range MIN_PRIORITY
to MAX_PRIORITY
.SecurityException
- if checkAccess()
determines that the current thread cannot modify this threadpublic final int getPriority()
The priority of a virtual thread is always NORM_PRIORITY
.
public final void setName(String name)
name
. First the checkAccess
method of this thread is called with no arguments. This may result in throwing a SecurityException
.
name
- the new name for this thread.SecurityException
- if the current thread cannot modify this thread.public final String getName()
public final ThreadGroup getThreadGroup()
null
if the thread has terminated. The thread group returned for a virtual thread is the special ThreadGroup for virtual threads.
null
public static int activeCount()
The value returned is only an estimate because the number of threads may change dynamically while this method traverses internal data structures, and might be affected by the presence of certain system threads. This method is intended primarily for debugging and monitoring purposes.
public static int enumerate(Thread[] tarray)
ThreadGroup.enumerate(Thread[])
method of the current thread's thread group. Virtual threads are not enumerated by this method. An application might use the activeCount method to get an estimate of how big the array should be, however if the array is too short to hold all the threads, the extra threads are silently ignored. If it is critical to obtain every live thread in the current thread's thread group and its subgroups, the invoker should verify that the returned int value is strictly less than the length of tarray
.
Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.
tarray
- an array into which to put the list of threadsSecurityException
- if ThreadGroup.checkAccess()
determines that the current thread cannot access its thread group@Deprecated(since="1.2", forRemoval=true) public int countStackFrames()
UnsupportedOperationException
.public final void join(long millis) throws InterruptedException
millis
milliseconds for this thread to terminate. A timeout of 0
means to wait forever. This method returns immediately, without waiting, if the thread has not been started
.this.wait
calls conditioned on this.isAlive
. As a thread terminates the this.notifyAll
method is invoked. It is recommended that applications not use wait
, notify
, or notifyAll
on Thread
instances.millis
- the time to wait in millisecondsIllegalArgumentException
- if the value of millis
is negativeInterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public final void join(long millis, int nanos) throws InterruptedException
millis
milliseconds plus nanos
nanoseconds for this thread to terminate. If both arguments are 0
, it means to wait forever. This method returns immediately, without waiting, if the thread has not been started
.this.wait
calls conditioned on this.isAlive
. As a thread terminates the this.notifyAll
method is invoked. It is recommended that applications not use wait
, notify
, or notifyAll
on Thread
instances.millis
- the time to wait in millisecondsnanos
- 0-999999
additional nanoseconds to waitIllegalArgumentException
- if the value of millis
is negative, or the value of nanos
is not in the range 0-999999
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public final void join() throws InterruptedException
An invocation of this method behaves in exactly the same way as the invocation
join(0)
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public final boolean join(Duration duration) throws InterruptedException
This method does not wait if the duration to wait is less than or equal to zero. In this case, the method just tests if the thread has terminated.
duration
- the maximum duration to waittrue
if the thread has terminated, false
if the thread has not terminatedInterruptedException
- if the current thread is interrupted while waiting. The interrupted status of the current thread is cleared when this exception is thrown.IllegalThreadStateException
- if this thread has not been started.public static void dumpStack()
public final void setDaemon(boolean on)
The daemon status of a virtual thread is always true
and cannot be changed by this method to false
.
This method must be invoked before the thread is started. The behavior of this method when the thread has terminated is not specified.
on
- if true
, marks this thread as a daemon threadIllegalArgumentException
- if this is a virtual thread and on
is falseIllegalThreadStateException
- if this thread is alive
SecurityException
- if checkAccess()
determines that the current thread cannot modify this threadpublic final boolean isDaemon()
true
.true
if this thread is a daemon thread; false
otherwise.@Deprecated(since="17", forRemoval=true) public final void checkAccess()
If there is a security manager, its checkAccess
method is called with this thread as its argument. This may result in throwing a SecurityException
.
SecurityException
- if the current thread is not allowed to access this thread.public String toString()
public ClassLoader getContextClassLoader()
ClassLoader
for this thread. The context ClassLoader
may be set by the creator of the thread for use by code running in this thread when loading classes and resources. If not set, the default is to inherit the context class loader from the parent thread. The context ClassLoader
of the primordial thread is typically set to the class loader used to load the application.
ClassLoader
for this thread, or null
indicating the system class loader (or, failing that, the bootstrap class loader)SecurityException
- if a security manager is present, and the caller's class loader is not null
and is not the same as or an ancestor of the context class loader, and the caller does not have the RuntimePermission
("getClassLoader")
public void setContextClassLoader(ClassLoader cl)
ClassLoader
for this thread. The context ClassLoader
may be set by the creator of the thread for use by code running in this thread when loading classes and resources.
If a security manager is present, its checkPermission
method is invoked with a RuntimePermission
("setContextClassLoader")
permission to see if setting the context ClassLoader is permitted.
cl
- the context ClassLoader for this Thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)SecurityException
- if the current thread cannot set the context ClassLoaderpublic static boolean holdsLock(Object obj)
true
if and only if the current thread holds the monitor lock on the specified object. This method is designed to allow a program to assert that the current thread already holds a specified lock:
assert Thread.holdsLock(obj);
obj
- the object on which to test lock ownershiptrue
if the current thread holds the monitor lock on the specified object.public StackTraceElement[] getStackTrace()
If there is a security manager, and this thread is not the current thread, then the security manager's checkPermission
method is called with a RuntimePermission("getStackTrace")
permission to see if it's ok to get the stack trace.
Some virtual machines may, under some circumstances, omit one or more stack frames from the stack trace. In the extreme case, a virtual machine that has no stack trace information concerning this thread is permitted to return a zero-length array from this method.
StackTraceElement
, each represents one stack frame.SecurityException
- if a security manager exists and its checkPermission
method doesn't allow getting the stack trace of thread.public static Map<Thread,StackTraceElement[]> getAllStackTraces()
StackTraceElement
that represents the stack dump of the corresponding Thread
. The returned stack traces are in the format specified for the getStackTrace
method. The threads may be executing while this method is called. The stack trace of each thread only represents a snapshot and each stack trace may be obtained at different time. A zero-length array will be returned in the map value if the virtual machine has no stack trace information about a thread.
If there is a security manager, then the security manager's checkPermission
method is called with a RuntimePermission("getStackTrace")
permission as well as RuntimePermission("modifyThreadGroup")
permission to see if it is ok to get the stack trace of all threads.
Map
from Thread
to an array of StackTraceElement
that represents the stack trace of the corresponding thread.SecurityException
- if a security manager exists and its checkPermission
method doesn't allow getting the stack trace of thread.@Deprecated(since="19") public long getId()
threadId()
instead.long
number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime.public final long threadId()
long
number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime.public Thread.State getState()
public static void setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler ueh)
Uncaught exception handling is controlled first by the thread, then by the thread's ThreadGroup
object and finally by the default uncaught exception handler. If the thread does not have an explicit uncaught exception handler set, and the thread's thread group (including parent thread groups) does not specialize its uncaughtException
method, then the default handler's uncaughtException
method will be invoked.
By setting the default uncaught exception handler, an application can change the way in which uncaught exceptions are handled (such as logging to a specific device, or file) for those threads that would already accept whatever "default" behavior the system provided.
Note that the default uncaught exception handler should not usually defer to the thread's ThreadGroup
object, as that could cause infinite recursion.
ueh
- the object to use as the default uncaught exception handler. If null
then there is no default handler.SecurityException
- if a security manager is present and it denies RuntimePermission
("setDefaultUncaughtExceptionHandler")
public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler()
null
, there is no default.public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler()
ThreadGroup
object is returned, unless this thread has terminated, in which case null
is returned.public void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler ueh)
A thread can take full control of how it responds to uncaught exceptions by having its uncaught exception handler explicitly set. If no such handler is set then the thread's ThreadGroup
object acts as its handler.
ueh
- the object to use as this thread's uncaught exception handler. If null
then this thread has no explicit handler.SecurityException
- if the current thread is not allowed to modify this thread.
© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Thread.html